Synthetic resin molded articles made from polymethyl methacrylate resins, polymethacrylimide resins, polycarbonate resins, polystyrene resins, AS resins, and the like are not only lightweight and excellent in impact resistance but also excellent in transparency and are being frequently used in various lamp lenses, glazing materials, covers for gauges, and the like as automotive plastic materials in recent years. In particular, as for headlamp lenses, use of the plastic materials is increasing owing to a tendency to lightweight automobiles for improving the fuel cost and diversification of design. On the other hand, these synthetic resin molded articles are susceptible to damages on their surfaces by contacting, wearing, scratching, or the like with other hard substances because mar resistance of their surfaces is insufficient, and damages generated on their surfaces lower their merchandise value. Further, in the case that these synthetic resin molded articles are used as the aforementioned automotive materials, weatherability is also an important performance. In particular, in the case of a polycarbonate resin and the like, weatherability thereof is insufficient and they are easily deteriorated by an active energy ray such as ultraviolet ray included in sunlight, and molded articles thereof are considerably yellowed or cracks are generated on the surfaces of the molded articles.
Various methods for improving such shortcomings of the synthetic resin molded articles have been conventionally investigated, and for example, a method in which a coating material composed of a silicone based or melamine based resin composition is coated on a surface of a synthetic resin molded article and subjected to heating condensation to form a crosslinked coating film, and hence mar resistance is improved and a method in which a resin composition composed of a radical polymerizable monomer is coated on a surface of a synthetic resin molded article and an active energy ray is irradiated on the resultant surface to form a crosslinked coating film have been proposed (Patent Document 1: Japanese Patent Application Laid-Open No. Sho 56-122,840).
Among these methods, a resin composition obtained by compounding substances such as a poly(meth)acrylate of a mono- or poly-pentaerythritol, a urethane poly(meth)acrylate compound having at least 2 radical-polymerizable unsaturated double bonds in a molecule, and a poly[(meth)acryloyloxyalkyl](iso)cyanurate in a specific proportion is proposed, and it is found that this resin composition can realize a compatibility of excellent mar resistance and weatherability (Patent Document 2: Japanese Patent Application Laid-Open No. Hei 05-230,397, Patent Document 3: Japanese Patent Application Laid-Open No. Hei 06-128,502).
However, further improvement in weatherability is desired for the purpose of use in a long period of time under a severe environment such as high humidity environment. While, a resin composition which is excellent in weatherability and contains a polyester type aliphatic urethanepoly(meth)acrylate compound composed of an aliphatic isocyanate compound having two isocyanate groups in a molecule, a caprolactone-modified polyester diol, and an acrylate having a hydroxyl group is proposed (Patent Document 4: Japanese Patent Application Laid-Open No. Hei 08-283,607, Patent Document 5: Japanese Patent Application Laid-Open No. Hei 08-283,608, Patent Document 6: Japanese Patent Application Laid-Open No. 2004-217,879)
However, the compositions described in these patent documents are not sufficient in mar resistance.
While, a resin composition containing a caprolactone-modified poly(meth)acrylate of a mono- or polypentaerythritol is proposed (Patent Document 7: Japanese Patent Application Laid-Open No. Hei 09-286,809, Patent Document 8: Japanese Patent Application Laid-Open No. Hei 04-311,714, Patent Document 9: Japanese Patent Application Laid-Open No. 2002-249,680). The composition described in Patent Document 7 contains a urethanepoly(meth)acrylate compound having 6 or more (meth)acrylolyoxy groups in a molecule and thereby weatherability of a cured material of the composition is improved. The composition described in Patent Document 8 contains a urethaneacrylate compound composed of an alicyclic dicarboxylic acid and a polyol and thereby weatherability of a cured material of the composition is improved. The composition described in Patent Document 9 uses a specific acryl-modified polyolefin and thereby an in-mold coating composition having excellent adhesion to a polyolefin base material and weatherability is obtained. In these patent documents, there is no description or suggestion of a conspicuous effect in which weatherability of a cured material of a composition is sharply improved by compounding a caprolactone-modified poly(meth)acrylate of a mono- or poly-pentaerythritol in the composition.
Patent Document 1: Japanese Patent Application Laid-Open No. Sho 56-122,840
Patent Document 2: Japanese Patent Application Laid-Open No. Hei 05-230,397
Patent Document 3: Japanese Patent Application Laid-Open No. Hei 06-128,502
Patent Document 4: Japanese Patent Application Laid-Open No. Hei 08-283,607
Patent Document 5: Japanese Patent Application Laid-Open No. Hei 08-283,608
Patent Document 6: Japanese Patent Application Laid-Open No. 2004-217,879
Patent Document 7: Japanese Patent Application Laid-Open No. Hei 09-286,809
Patent Document 8: Japanese Patent Application Laid-Open No. Hei 04-311,714
Patent Document 9: Japanese Patent Application Laid-Open No. 2002-249,680